<p>
  A function is a reusable block of code. We can use a function to output a value, or do anything else we want. We can easily define our own function by using the keyword "def".
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<pre class="python">def product(x,y):
    return x*y
print product(2,3)
[out]: 6
print product(5,10)
[out]: 50
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<p>
  The keyword "def" is followed by the function name and the parenthesized list of formal parameters. The statements that form the body of the function start at the next line, and must be indented. The product() function above has "x" and "y" as its parameters. A function doesn't necessarily have parameters:
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<pre class="python">def say_hi():
    print "Welcome to QuantConnect'
say_hi()
[out]: Welcome to QuantConnect
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